Elastic Origin of the Unsymmetrical Thermal Hysteresis in Spin Crossover Materials: Evidence of Symmetry Breaking

Ndiaye, Mamadou; Belmouri, Nour El Islam; Linarès, Jorge; Boukheddaden, Kamel

doi:10.3390/sym13050828

Cited by 15 publications

(11 citation statements)

References 70 publications

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“…The Hamiltonian describing this system of two coupled 1D chains, taking accounting for the electronic and elastic degrees of freedom [36][37][38][39][40], writes:…”

Section: The Electro-elastic Modelmentioning

confidence: 99%

Electro-elastic Modeling of Multi-Step Transitions in two Elastically Coupled and Sterically Frustrated 1D Spin-Crossover Chains

Traiche¹,

Oubouchou²,

Boukheddaden³

2023

Preprint

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1D spin crossover (SCO) solids which convert between the low-spin (LS) and the high-spin (HS) states are widely studied in the literature due to their diverse thermal and optical characters which allows obtaining many original behaviors, such as large thermal hysteresis, incomplete spin tran-sitions, as multi-step spin transitions with self-organized states. In the present work, we investigate the thermal behaviors of a system of two-elastically coupled 1D mononuclear chains, using the electro-elastic model, by including an elastic frustration in the nearest neighbors (nn) bond length distances of each chain. The chains are made of SCO sites that are coupled elastically through springs with their nn and next-nearest neighbors. The elastic inter-chain coupling includes diagonal springs, while the nn inter-chains distance is fixed to that of the high-spin state. The model is solved using MC simulations, performed on the spin states and the lattice distortions. When we only frustrate the first chain, we found a strong effect on the thermal-dependence of the HS fraction of the second chain, whose, by lowering its transition temperature which is also accompanied with the appearance of a significant residual HS fraction at low temperature. In the second step, we frustrate both chains by imposing different frustration rates and found that, for high frustration values, the thermal dependence of the total HS fraction exhibits three step and even four step spin transitions. The careful examination of the spin state structures in the plateau regions revealed the existence of special antiferro-elastic structure of type LSLS-HSHS-LSLS-HSHS along the first chain, and HSHS-LSLS-HSHS-LSLS along the second, also showing that the two chains seem to be antifer-ro-elastically coupled. This type of organization is interesting, because it anticipates the possible existence of periodic structures made of alternate 1D antiferro-like HS-LS strings coupled in the ferro-like fashion along the interchain direction in the 2D case.

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“…The Hamiltonian describing this system of two coupled 1D chains, taking accounting for the electronic and elastic degrees of freedom [36][37][38][39][40], writes:…”

Section: The Electro-elastic Modelmentioning

confidence: 99%

Electro-elastic Modeling of Multi-Step Transitions in two Elastically Coupled and Sterically Frustrated 1D Spin-Crossover Chains

Traiche¹,

Oubouchou²,

Boukheddaden³

2023

Preprint

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“…r i,i+2 ) by an invariant distance x (resp. y) in the lattice [83]. We denote by x relax L2L2 and x relax L2H2 (resp.…”

Section: Analytical Expressions Of the Relaxed Lattice Bond Lengthsmentioning

confidence: 99%

Elastic Modeling of Two-Step Transitions in Sterically Frustrated 1D Binuclear Spin-Crossover Chains

2021

Self Cite

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Among the large family of spin-crossover materials, binuclear systems play an important role due to their specific molecular configurations, allowing the presence of multi-step transitions and elastic frustration. Although this issue benefited from a significant number of spin-based theories, there is almost no elastic description of the spin transition phenomenon in binuclear systems. To overcome this deficiency, in this work we develop the first elastic modeling of thermal properties of binuclear spin-crossover solids. At this end, we investigated a finite spin-crossover open chain constituted of elastically coupled binuclear (A = B) blocks, , in which the considered equivalent A and B sites may occupy two configurations, namely low-spin (LS) and high-spin (HS) states. The sites of the binuclear unit interact via an intramolecular spring and couple to the neighboring binuclear units via other springs. The model also includes the change of length inside and between the binuclear units subsequent to the spin state changes. When injecting an elastic frustration inside the binuclear unit in the LS state, competing interactions between the intra- and the inter-binuclear couplings emerge. The latter shows that according to the intra- and inter-binuclear elastic constants and the strength of the frustration, multi-step transitions are derived, for which a specific self-organization of type (HS = HS)-(LS-LS)-(HS = HS) is revealed and discussed. Finally, we have also studied the relaxation of the metastable photoinduced HS states at low temperature, in which two relaxation regimes with transient self-organized states were identified when monitoring the elastic frustration rate or the ratio of intra- and intermolecular elastic interactions. These behaviors are reminiscent of the thermal dependence of the order parameters of the system. The present model opens several possibilities of extensions of elastic frustrations acting in polynuclear spin-crossover systems, which may lead to other types of spin-state self-organizations and relaxation dynamics.

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“…The interactions between molecular units may be modelled with mechanistic toy models based on Ising-like Hamiltonians [electro-lattice models, e.g. Ndiaye et al (2021)], as by its very nature this approach neglects many intra-molecular degrees of freedom. For any real spin crossover material however, change of properties associated with the change of spin states can neither be reduced to a behaviour of an isolated individual molecule nor simplified to mechanistic models; this is why, together with theoretical modelling, the structural experiment remains the most important source of information on the microscopic processes comprising spin crossover phenomena (Pillet, 2021).…”

Section: Introductionmentioning

confidence: 99%

Preliminary observations of the interplay of radiation damage with spin crossover

Chernyshov¹,

Dyadkin²,

Törnroos³

2022

Acta Crystallogr Sect B

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Intense synchrotron radiation makes time-resolved structural experiments with increasingly finer time sampling possible. On the other hand, radiation heating, radiation-induced volume change and structural disorder become more frequent. Temperature, volume change and disorder are known to be coupled with equilibrium in molecular spin complexes, balancing between two or more spin state configurations. Combining single-crystal diffraction and synchrotron radiation it is illustrated how the radiation damage and associated effects can affect the spin crossover process and may serve as yet another tool to further manipulate the spin crossover properties.

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Elastic Origin of the Unsymmetrical Thermal Hysteresis in Spin Crossover Materials: Evidence of Symmetry Breaking

Cited by 15 publications

References 70 publications

Electro-elastic Modeling of Multi-Step Transitions in two Elastically Coupled and Sterically Frustrated 1D Spin-Crossover Chains

Electro-elastic Modeling of Multi-Step Transitions in two Elastically Coupled and Sterically Frustrated 1D Spin-Crossover Chains

Elastic Modeling of Two-Step Transitions in Sterically Frustrated 1D Binuclear Spin-Crossover Chains

Preliminary observations of the interplay of radiation damage with spin crossover

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